Losses in cholinergic and other neurotransmitter systems have been well documented in Alzheimer's disease and some of these changes have been correlated with cognitive dysfunctions which occur. Current pharmacological strategies which target the replacement of deficient neurotransmitters have met with limited success, partly due to problems associated with systemic administration such as non-specific drug localization. In Project 2 of this Program Project Proposal, genetically modified cells will be developed for use as intracerebral delivery vehicles of neurotransmitters found to be deficient in the brain of humans with Alzheimer's disease. Primary dermal fibroblasts will be transduced with cDNAs for choline acetyltransferase, aromatic L-amino acid decarboxylase and tryptophan hydroxylase. Transduced fibroblasts will be examined in vitro to characterize the expression of the transgenes and the production and release of neurotransmitters. Transduced fibroblasts will then be implanted within the brain to assess the survival of the cells, stability of the transgenes and the production of neurotransmitters in vivo. Finally, animal models of cognitive dysfunction will be used to assess the functional efficacy of neurotransmitter-producing fibroblasts within the brain. The performance of young rats with selective lesions of cholinergic and/or serotonergic afferents to the hippocampus and cognitively impaired aged rats will be assessed on spatial learning and memory tasks following the intracerebral implantation of acetylcholine- and/or serotonin-producing fibroblasts. These studies will provide an understanding of the role of various neurotransmitters in cognition and contribute to the continued development of the gene transfer/intracerebral grafting technique as an alternative approach to the treatment of cognitive dysfunctions.